This invention relates generally to inkjet printers. More specifically, the invention relates to a technique for substantially reducing vertical banding from printing operations performed by inkjet printers that utilize vacuum fans.
FIG. 1 illustrates a conventional large format inkjet printer 110 having a pair of legs 114, left and right sides 116, 118, and a cover 122. This example will be used to illustrate some of the problems associated with known large format inkjet printers. As illustrated in FIG. 1, the printer 110 includes a carriage 100 supporting a plurality of printheads 102-108. The carriage 100 is coupled to a slide rod 124 with a coupling 125. As is generally known to those of ordinary skill in the art, during a printing operation, the carriage 100 travels along the slide rod 124 generally in a Y-axis direction 103 to make a printing pass. In addition, as the carriage 100 travels along the Y-axis 103, certain of the printheads 102-108 drop ink onto a medium 130, e.g., paper, through a plurality of nozzles (not shown). At certain times during the printing operation, the medium 130 typically travels generally in a X-axis direction 101. By virtue of performing a plurality of printing passes over the medium 130 by the carriage 100 in the above-described manner, an image, e.g, plot, text, and the like, may be printed onto the medium.
Also illustrated in FIG. 1 is a printer control panel 120 located on a right side 118 of the large format inkjet printer 110. The printer control panel 120 typically functions as an interface between a user and the printer 110 to enable certain printer operations to be set (e.g., medium advance, printmode, etc.). In addition to housing the printer control panel 120, the right side 118 of the printer 110 typically also houses printer components for performing printing operations (e.g., printer electronics, a service station for servicing operations on the printheads 102-108, etc.).
During a printing operation, the accuracy of ink drop placement onto the medium 130 may be relatively compromised by virtue of a plurality of factors. For example, small inaccuracies due to uncontrolled movements, oscillations, etc., may cause faults in the printing output to become visible. In this respect, the printing quality may be adversely affected by operation of electromechanical components, e.g., vacuum fans, coupled to the printers. For example, operation of these types of electromechanical components may cause the printers to suffer from some of the above-stated inaccuracies. That is, during the operation of these types of electromechanical components, the electronic components may have a tendency to vibrate at certain frequencies, thus causing other components, e.g., printheads 102-108, of the printers to undergo uncontrolled movements at a periodic rate. One result of the uncontrolled movements at a periodic rate is that vertical bands may be created in the printed image, e.g., plot, text, and the like.
In order to overcome some of the problems associated with misalignment of fired ink drops during printing operations, many inkjet printers have employed what is known as a multi-pass print mode. In a multi-pass print mode, instead of performing a single pass over a print swath, two or more passes are made with different nozzles to fire ink drops during each pass. In this respect, in a four pass print mode, for example, only one of four ink droplets may be missing or misdirected resulting in a much less catastrophic result. While the multi-pass printing technique has improved image quality for those situations in which failed nozzles are present, this technique has been relatively unsuccessful in removing vertical bands resulting from vibrations caused by operation of the above-described electromechanical components. In one respect, the source of vertical banding may not be successfully randomized with the increased number of passes. That is, the vibrations that are coupled to the carriage 100 may typically result in dot placement errors (DPE) of the same spatial frequency. Thus, the DPE have a tendency to accumulate when a multi-pass print mode is utilized, resulting in the formation of vertical bands.
Referring now to FIG. 2, which is an enlarged sectional view of the printer 110 illustrated in FIG. 1, with the cover 122 removed, an example of an electromechanical component that may cause vertical banding is shown. As shown in FIG. 2, a space is formed between the left and right sides 116, 118 of the printer 110 defining an area in which the medium (not shown) may be printed upon. Generally extending along the print area is a serpentine-shaped opening 126 for applying vacuum pressure on a lower surface of the medium (not shown). In this respect, air is drawn in through the serpentine opening 126 to generally maintain the position of the medium in the print area.
Referring now to FIG. 3, which is a sectional view of the printer 110 generally below the print area, a vacuum fan 140 is illustrated. As stated hereinabove, the vacuum fan 140 is an example of an electromechanical component whose operation may cause the print quality to be adversely affected by its operation. As illustrated in FIG. 3, the vacuum fan 140 typically operates to draw air from the serpentine-shaped opening 126 and through an underside of the printer 110. When the vacuum fan 140 is activated and is in operation, the vacuum fan typically rotates at a certain frequency, depending upon the amount of voltage supplied to the vacuum fan.
At least by virtue of the direct coupling between the vacuum fan 140 and the printer 110, the rotation of the vacuum fan causes the printer to vibrate at a certain degree corresponding to the frequency of rotation of the vacuum fan. One result of the vibration is that the printheads 102-108 may undergo uncontrolled movements at certain times during a printing operation. Typically, the uncontrolled movements occur at a periodic rate, often due to the periodic nature of the vibrations, oftentimes resulting in the uncontrolled movements occurring at the same or substantially similar locations along each printing pass, thus resulting in the formation of vertical bands.
One solution to the above-stated problem of vertical band formation has been to attempt to substantially mechanically isolate the vacuum fan 140 from the printer 110 and thus attempt to prevent the vibrations caused in the operation of the vacuum fan from affecting the other components of the printer, namely the operation of the printheads 102-108. However, even relatively substantial mechanical isolation of the vacuum fan 140 from the printer 110 has been found to be relatively insufficient in preventing the translation of the vibrations to other printer components. In addition, it has been found that the attempt to substantially mechanically isolate the vacuum fan 140 from the printer 110 typically increases the costs in fabricating the printer by relatively large amounts. Thus, even substantial mechanical isolation of the vacuum fan 140 from the printer 110 has not proven to be a substantially viable solution to some of the vertical band formation problems that may occur during printing operations.
According to one aspect, the present invention pertains to a method for reducing vertical banding in a printing device having a printhead for printing onto a medium and a voltage receiving component coupled to the printing device, in which, operation of the voltage receiving component may cause the voltage receiving component to vibrate at a frequency of oscillation that is configured to vary according to the degree of voltage supplied to the voltage receiving component. In the method, a first voltage is supplied to the voltage receiving component and a printing pass is performed over the medium. In addition, the first voltage supplied to the voltage receiving component is varied to a second voltage in order to vary the frequency of oscillation of the voltage receiving component. Moreover, the second voltage is supplied to the voltage receiving component, and another printing pass is performed over the medium.
According to another aspect, the present invention pertains to a method for reducing vertical banding in a printing device having a printhead for printing onto a medium and a voltage receiving component coupled to the printing device, in which operation of the voltage receiving component may cause the voltage receiving component to vibrate at a frequency of oscillation that is configured to vary according to the degree of voltage supplied to the voltage receiving component. In the method, a printing pass is performed over the medium at a first speed. In addition, the first speed is varied to a second speed, such that the second speed is not equal to the first speed. Moreover, another printing pass is performed over the medium at the second speed.
According to yet another aspect, the present invention relates to a computer readable storage medium on which is embedded one or more computer program(s), the one or more computer program(s) implementing a method for reducing vertical banding during a printing operation of a printer. The one or more computer program(s) include a set of instructions for supplying a first voltage to a voltage receiving component, performing a first printing pass over a medium, and varying the first voltage supplied to the voltage receiving component to a second voltage to thereby vary a frequency of oscillation of the voltage receiving component. The one or more computer program(s) also include a set of instructions for supplying the second voltage to the voltage receiving component and performing another printing pass over the medium.
Certain embodiments of the present invention are capable of achieving certain advantages, including, the relative reduction in the formation of vertical bands during a printing process.